1. Field of the Invention
This invention relates to double heterostructure (DH) light emitting diodes, and more particularly, to DH junction lasers or spontaneous emission diodes which emit radiation in the infrared region.
2. Description of the Prior Art
The advancement of optical communications technology depends on the development of inexpensive and reliable components, i.e., optical sources, receivers, detectors and transmission means. A major advancement in the field was the development of low loss optical fibers for transmission of optical signals. For example, the silica fibers currently in use transmit light and exhibit low loss on the order of 1-2 db/km in the near infrared region from about 0.7 to 2 micrometers wavelength. In order to exploit such fibers, the optical sources should emit light in the wavelength region where the fibers exhibit fairly low loss. Thus, a second significant advance in this technology was the development DH junction lasers which operate CW at room temperature. The lowest threshold and more reliable DH lasers today are fabricated from the Al.sub.x Ga.sub.1-x As-GaAs system and emit in the range of about 0.8 to 0.9 micrometers.
Briefly, the DH laser comprises a narrow bandgap active region which may be either n- or p-type, or contain a p-n junction. The active region is sandwiched between relatively wider bandgap, opposite-conductivity-type cladding layers which form two heterojunctions, one at each interface with the active region. These heterojunctions serve to confine injected carriers, as well a stimulated radiation, to the active region. Consequently, the heterojunctions should have as few defects as possible since such defects act as nonradiative recombination centers and tend to reduce efficiency and increase lasing thresholds. Thus, it is important that the layers be nearly lattice matched at the growth temperature and at the operating temperature of the laser. The need for lattice-matched materials is another reason why the Al.sub.x Ga.sub.1-x As-GaAs system has been so intensively studied; the lattice constants for Al.sub.x Ga.sub.1-x As and GaAs are approximately equal for all values of x. Thus, highly quality heterojunctions can be formed.
Recently a novel fiber comprising zinc chloride has been discovered and described by W. H. Grodkiewicz et al in U.S. application Ser. No. 885,198, filed on Mar. 10, 1978, and assigned to the assignee hereof. This fiber is capable of transmitting radiation in the range of 1-7 micrometers. However, from about 3.0 to 4.5 micrometers the fiber exhibits extremely low loss on the order of 10.sup.-3 db/km. Therefore, an optical source which emits radiation in this wavelength range would be of great interest.